A variety of data transmission and storage schemes using telephone systems are available. These schemes normally require that the data transfer be done synchronously, i.e., that a known signal begins at a known location in a data stream and transmits through to a known end. Synchronicity is typically insured using a two-way handshake protocol. At the receiver, some hardware is dedicated to demodulating the received data and converting it to a binary signal, while other hardware is dedicated to the tasks of conducting the handshake and of assembling, sorting, and storing the data. These functions are all duplicated at the transmitter as well. The conventional transmission and storage schemes require expensive complex equipment at both the transmitting and receiving ends, together with two-way communication capability.
The expense and complexity of equipment required for existing schemes make it difficult to produce a portable information display which can be easily updated over the telephone, yet is still compact enough to be tucked in a pocket or purse.